The composition of atherosclerotic plaques in 733 five-mm segments of the 4 major (left main, left anterior descending, left circumflex, and right) epicardial coronary arteries of 18 patients >90 years of age was determined by computerized planimetric analysis. By analysis of all coronary segments of all patients 90, the plaques consisted primarily of fibrous tissue (87+/-8%) with calcific deposits (7+/-6%), pultaceous debris (5+/-4%) and foam cells (1+/-1%) occupying a much smaller percentage of plaque area. Analysis of composition according to the 4 degrees of luminal cross-sectional area narrowing showed marked step-wise increases in pultaceous debris (from 0+/-0% at 0-25% narrowing to 18+/-22% at 76-100% narrowing, P=0.0001) and calcific deposits (from 0+/-0% to 10+/-15%, p=0.002), and decreases in fibrous tissue (99+/-3% to 71+/-23%, p=O.0001) and area occupied by the media (from 35+/-8% to 16+/-8%, p=0.0001). When restricting the analysis to sections narrowed >75%, no significant differences were found in plaque components or medial area between patients with (11 patients) and without (7 patients) myocardial infarcts at necropsy.